Hybrid Suspension/Solution Precursor Plasma Spraying of a Complex Ba(Mg_1/3Ta_2/3)O₃ Perovskite: Effects of Processing Parameters and Precursor Chemistry on Phase Formation and Decomposition

Ba(Mg_1/3Ta_2/3)O₃ (BMT) has a high melting point and is envisioned as a thermal barrier coating material. In this study, a hybrid suspension/solution precursor plasma spray process with a radio frequency thermal plasma torch is designed to deposit BMT nanostructured coatings. Six combinations of chemical reagents are investigated as coating precursors: one BMT powder suspension and five Ta₂O₅ suspensions in nitrate- or acetate-based solutions. X-ray photoelectron spectroscopy is used to evaluate the element evaporation during plasma spraying, while a thermogravimetric/differential thermal analysis is applied to investigate the BMT formation. Parameters such as precursor chemistry, plasma power, spraying distance and substrate preheating are studied with regard to the coating phase structure. Twice the Mg stoichiometric amount with a power of 50 kW shows the best results when using nanocrystallized Ta₂O₅ as a tantalum precursor. When choosing nitrates as Ba and Mg precursors, crystallized BMT is obtained at lower plasma power (45 kW) when compared to acetates (50 kW). BaTa₂O₆, Ba₃Ta₅O₁₅, Ba₄Ta₂O₉, Mg₄Ta₂O₉ are the main secondary phases observed during the BMT coatings deposition. Because of the complicated acetate decomposition process, the coating deposition rate from nitrate precursors is 1.56 times higher than that from acetate precursors.